In 1991, S. Iijima (Nature, vol. 354: 56-58) reported growth of multi-wall coaxial nanotubes, containing 2-50 layers with radial separations of about 0.34 nm, using an arc discharge evaporation method similar to that used for Fullerene synthesis. The nanotubes originally observed by Iijima were formed on the negative voltage end of a carbon electrode and were plentiful in some regions and sparse in other regions. Since that time, other workers have developed other discharge means for controlled deposition of graphitic carbon. However, it is not straightforward to control the growth of or density of, single wall nanotubes (“SWCNTs”), multi-wall nanotubes (“MWCNTs”) and/or carbon-based nanofibers (“CNFs”).
Recently, interest has grown in use of arrays of carbon nanotubes (“CNTs”) as an intermediary for transport of electrical particles (e.g., electrons) and/or transport of thermal energy from one body to another. For example, a CNT array may be used for dissipation of thermal energy or accumulated electrical charge associated with operation of an electronics device or system. However, the device or system connected to the CNT array(s) may require use of different CNT array densities and/or different CNT tower heights in different regions, because of differing transport requirements. Use of a mask to discriminate between a CNT growth region and a no-growth region has been demonstrated. However, this approach only produces different regions where CNTs are present (with a substantially constant density) and where CNTs are absent (density substantially 0).
What is needed is a method and system for controlling density and/or tower height of CNTs grown on a substrate, where the CNT density and/or the CNT average tower height are allowed to vary from one location to another. Preferably, the approach should allow imposition of tight or loose local variations of density and/or tower height, depending upon the relative tightness of growth through local temperature control. Preferably, the approach should allow variation, by a factor of 1-10, in the local CNT density, and a factor of 100-300, in the local CNT average tower height.